For erecting a wind turbine tower usually two cranes are needed to keep the moment of tilt under control when the tower reaches the vertical position. Just before reaching the vertical position the moment acting on the tower induced by gravitational force acts on a side of the tower and tends to tilt it in a more horizontal position. When reaching the vertical position, the tower may swing over. Such a swing over could lead to a dangerous swinging of the tower. Furthermore, it could induce unwanted loads onto the tower. Usually therefore a second crane is used to keep the tower under control and to prevent it from swinging due to the tilt moment. The first crane would be attached to the flange at the top of the tower, the second crane to the bottom flange of the tower. Then, the first crane would raise the top of the tower and second crane would keep the bottom of the tower clear of the ground. When the tower is hanging in an upright position, a technician needs to move under the hanging tower to remove the hook or lifting bracket(s) from the bottom flange. However, it would be desirable to use only one crane to erect the tower and thereby save the direct and indirect costs of the second crane. In particular, it would be desirable to overcome the need for the crane at the bottom end of the tower.
U.S. Pat. No. 6,408,575 B1 and U.S. Pat. No. 6,782,667 B2 describe methods for erecting wind turbine towers which are pivotably connected to a base foundation. These towers could, in principle, be erected with only one crane. However, the hinge at which a tower is pivotably connected to the foundation and the foundation itself would experience considerable loads during the erection of the tower. In particular, the load at the moment of swing over would lead to rather high forces on the hinge entailing the risk of damaging the hinge.